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Manual de la WHO

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    Manual de la WHO Manual de la WHO Document Transcript

    • WHO/CTD/SIP/98.2 Page 1I AIM OF THE MANUALThis manual and the accompanying slide set have been developed to assist inthe training of laboratory technicians and health workers in identifyingmedically relevant helminth eggs and larvae, and protozoal trophozoites andcysts. This manual complements the Bench Aids for the Diagnosis ofIntestinal Parasites (produced by the World Health Organization in 1994)and should ideally be used together when training health personnel. TheBench Aids were developed to aid laboratory technicians and other healthstaff in diagnosing intestinal parasitic infections from faecal samples. Theycontain nine plates of photomicrographs of the diagnostic stages of the mostcommon human intestinal parasites and descriptions of the laboratoryprocedures employed.When teaching laboratory methods it is essential for the tutor to demonstratehow these techniques are applied in the examination of stool specimens. It isalso important, that the learners do these procedures themselves to gain thenecessary confidence and ease of dealing with the procedures as they willhave to work without supervision after the training. Objectives of the training At the end of the training course, the learners should be able to: • perform specific laboratory techniques: - direct faecal smear; - Kato-Katz cellophane thick faecal smear technique; - faecal formalin ether/ethyl-acetate/gasoline concentration procedures; - staining techniques for intestinal protozoa; • identify intestinal parasites by genus and species; • quantify helminth eggs in faeces by Kato-Katz procedure.
    • WHO/CTD/SIP/98.2Page 2II USE OF THE MANUALThis manual may serve as a guide to conducting a workshop utilizing thetutor’s own expertise in the diagnosis of intestinal parasites with additionalbackground information provided in the Bench Aids. Topical outlines of thevarious subjects to be covered, and a list of required equipment andlaboratory supplies is provided.While this manual covers most pathogenic intestinal parasites it is highlyrecommended that the tutor concentrates mainly on the locally relevantparasites.The slide set used to illustrate the manual is based on the Bench Aids.However, the slides are not in the same order and additional slides have beenincluded. In part VIII, -Inventory of Slide Set-, slides have been arrangedand numbered according to the sequence proposed for presentation.Corresponding figures in the Bench Aids have also been identified andincluded. The numbering of the corresponding figures in the Bench Aidsfollows the same pattern in all plates, i.e. plate number, followed by thesequence on the plate (first figure is on the top left, last figure is on thebottom right). In figures presenting two different photomicrographs, a and bwill refer to the left and right image respectively.
    • WHO/CTD/SIP/98.2 Page 3
    • WHO/CTD/SIP/98.2Page 4IV LIST OF EQUIPMENT AND SUPPLIESSlide projectorMicroscopes (with a calibrated ocular micrometer)Bench centrifugeStaining jarsKato-Katz kitsSaline and iodine solutionsFormalin or formaldehyde (or gasoline)Glassware (centrifuge tubes)Slides (glass) and coverslips (plastic)Marking (grease) pencilsPipettesContainers for faecal samplesTrichrome stain solutionsPaper cups and applicator sticksDistilled waterImmersion oilPositive stool samplesV LIST OF ESSENTIAL PUBLICATIONSBench Aids for the diagnosis of intestinal parasites (WHO, 1994)(one for each participant)Basic Laboratory Methods in Medical Parasitology (WHO, 1991)(one for each tutor and facilitator)
    • WHO/CTD/SIP/98.2 Page 5VI MEDICALLY RELEVANT HELMINTHSHelminths include the nematodes (roundworms), trematodes (flukes) and thecestodes (tapeworms). Representatives of each of these groups are importanthuman parasites. The adult worms, that inhabit the intestine, discharge theeggs or larvae they produce in faeces. Therefore, diagnosis is based on thedetection of eggs or larvae in faecal samples.1. Overview of NematodesAscaris lumbricoidesMore than 1.3 billion people worldwide have ascariasis, and 250 millionsuffer from associated morbidity. Adult Ascaris lumbricoides live in thesmall intestine. Female worms measure as much as 35 cm in length, malesare smaller. Female worms produce over 200,000 eggs per day. Eggs maybe found easily in direct smears (2 mg) of faeces. The fertile unembryonatedegg measures 55-75 µm by 35-50 µm. It is brown in colour and the surfaceof the shell has conspicuous “bumps” called mamillations. The egg containsa single-cell ovum (Slide 1). Eggs may vary slightly in their appearance(Slide 2) but key features (size, mamillations) are always evident.Occasionally infertile female worms produce “infertile” eggs that aremorphologically different from the typical fertile egg . The contents of theeggs are irregular and disorganized (Slides 3 and 4). Infertile eggs are larger(Slide 5). They measure 85-95 µm by 43-47 µm, mamillations may beirregular and sometimes are absent. In rare cases, eggs are produced whichlack the surface, mamillated layer. These eggs are called “decorticated” eggs(Slide 6). They are about the same size as other fertile eggs and contain thesingle-cell ovum.
    • WHO/CTD/SIP/98.2Page 6Trichuris trichiuraTrichuriasis afflicts about 1 billion people throughout the world. AdultTrichuris trichiura are small, females are about 50 mm in length and malesslightly smaller. The anterior 2/3 of the body is slender and threaded intothe mucosa of the caecum and colon. The posterior end is thick, giving a“whiplike” shape to the worm; hence the name whipworm. Female wormsproduce eggs which are excreted in faeces. They have distinct featureswhich identify them. Eggs (Slides 7 and 8) measure 50-55 µm by 22-24 µm,have an oval shape and “plug-like” prominences at each pole. The shell isusually dark brown in colour and smooth. It contains a single-cell ovum.Note that the egg is smaller than that of A. lumbricoides (Slide 9). Becausefemale worms produce smaller numbers of eggs, they are often present infaeces in smaller numbers than A. lumbricoides eggs.HookwormsHookworms infect over 1.25 billion people throughout the world. Thehookworms (Necator americanus, Ancylostoma duodenale) are medicallyimportant human parasites and cause serious morbidity in many parts of theworld. The adult worms are small and live in the small intestine. Theymeasure about 1.0 to 1.5 cm in length. Although the adult worms of thesetwo species are easily identified on the basis of presence of cutting plates(N. americanus) or teeth (A. duodenale) around the mouth, the eggs theyproduce are nearly identical. The typical hookworm egg measures60 - 75 µm by 36 - 40 µm (Slides 10, 11 and 12). It has a clear, thin shelland the ovum is usually in the 4 or 8 cell stage or sometimes more advanced(Slide 11). Note in this image (Slide 13) the relative sizes ofA. lumbricoides, T. trichiura and hookworm eggs.There are other strongyle parasites which produce hookworm-like eggswhich must be dealt with in the course of this training as well.
    • WHO/CTD/SIP/98.2 Page 7TrichostrongylesSpecies of Trichostrongylus are usually small worms, less than 1 cm inlength that live in the small intestine and are of minor importance as humanparasites. However, their eggs are hookworm-like. Typically,trichostrongyle eggs resemble the eggs of the hookworms but are larger, 70-95 µm by 40-50 µm (Slide 14). The thin shell is slightly pointed rather thanflattened at one pole and the ovum is in a more advanced state ofsegmentation than is seen in hookworm eggs.Oesophagostomum species and Ternidens speciesThese two parasites produce hookworm-like eggs that tend to be larger thanhookworm eggs. The adult worms are somewhat larger than those of eitherN. americanus or A. duodenale and both live primarily in the colon of peopleliving in Africa. Oesophagostomum bifurcum eggs are only slightly largerthan hookworm eggs whereas eggs of Ternidens deminutus measure 85 µmby 50 µm (Slide 15). In both, the ovum is in an advanced state ofsegmentation and nearly fills the shell.Strongyloides stercoralisThis is an important nematode parasite of humans because of its ability toautoinfect and disseminate throughout the organ systems ofimmunocompromized or immunosuppressed individuals or others withmalignancies, e.g. lymphoma. This nematode parasite produces rhabditoidlarvae (Slides 16 and 17) instead of eggs, which are found in faeces. Thelarva measures 180-380 µm in length by 14 - 20 µm in diameter. It has ashort buccal capsule, a slender, pointed tail and a prominent genitalprimordium. The larva is easily recognized, either stained with iodine (Slide16) or not (Slide 17).2. Overview of TrematodesThe trematodes are usually referred to as flukes. They are solid-bodiedworms, hermaphroditic (except schistosomes) and have a complicated lifecycle that always involves a snail intermediate host as well as, in manyinstances, a second intermediate host. Depending on the species, trematodesinhabit the intestine, liver, lungs or blood vessels of their hosts.
    • WHO/CTD/SIP/98.2Page 8Schistosoma speciesThe schistosomes cause the most important trematode infections. Theyinfect over 200 million people. These worms live in the small blood vesselsassociated with the liver, intestine and bladder (depending on the species)and cause extreme pathology, morbidity and even death in individuals withheavy, chronic infections. They have a snail intermediate host andtransmission is water-related. All of the schistosome species produce non-operculated eggs which are discharged in faeces or urine (depending on thespecies), and each egg has a spine on some part of the shell.Schistosoma mansoni is most common in Africa but occurs in the Americasas well. The egg is discharged in faeces but typically in small numbers. Theegg is large, has a relatively thin shell with a conspicuous lateral spine(Slides 18, 19, 20 and 21). S. mansoni are also easily identified in Kato-Katzpreparations due to their size and presence of a lateral spine (Slide 18). Theegg measures 114 - 175 µm by 45 - 70 µm and contains a larva called themiracidium. Occasionally, the egg may be oriented in a way that hides thespine (Slide 20); tapping the cover glass on the preparation will oftenreorient the egg and reveal the spine.Schistosoma japonicum is transmitted in Asia. The egg which is found infaeces measures 70-100 µm by 55-65 µm, has a thin shell with an ofteninconspicuous, small lateral spine. The egg contains a miracidium (Slides 22and 23). The shell is sticky, causing debris to adhere to the surface andmaking it more difficult to identify.Schistosoma mekongi is closely related to S. japonicum and is transmitted inareas of Laos, Cambodia and Thailand. The egg is very similar to that of S.japonicum but is smaller, measuring 51-78 µm by 39-66 µm (Slide 25).Schistosoma haematobium is transmitted in Africa and the Middle East. Itdiffers from the others in that eggs are found in urine and sometimes inbiopsies of the bladder and rectum. The egg is large (112-170 µm by 40-70µm), thin shelled and has a terminal spine (Slides 26 and 27). It alsocontains a miracidium. In rare cases, eggs of S. haematobium are also foundin faeces.
    • WHO/CTD/SIP/98.2 Page 9Schistosoma intercalatum is restricted in its geographic distribution to Westand Central Africa. The egg resembles that of S. haematobium in that it hasa terminal spine (Slide 28) and is found in faeces rather than urine. It is verylarge, measuring 140-240 µm long, has an equatorial bulge and contains amiracidium.Foodborne TrematodesThere are a number of species of foodborne trematodes or flukes that live inthe liver and produce operculate eggs that are shed in faeces.Clonorchis sinensis is transmitted in Asia. The parasite is easily recognizedby its small egg (Slide 29) that measures 27-35 µm by 12-19 µm. Theoperculum is seated on a prominent rim or shoulder. At the opposite polethere may be a small protuberance. The egg contains a miracidium.The related liver fluke, Opisthorchis viverrini, is transmitted in SoutheastAsia and parts of Europe and produces an egg almost indistinguishable fromthat of C. sinensis (Slide 30).Fasciola hepaticaThis liver fluke is transmitted throughout the world, especially in sheep-raising countries. The adult fluke is large (about 3 cm), lives in the biliaryducts and produces eggs which are discharged in faeces. The egg is large,measuring 130-150 µm by 63-90 µm, has a thin shell that is brown in colour,a small operculum and is unembryonated when passed in faeces (Slide 31).The related intestinal fluke, Fasciolopsis buski, which occurs in Asia has anegg almost indistinguishable from that of F. hepatica. The F. buski egg(Slide 32) lacks the thickening at the abopercular end of the shellcharacteristic of F. hepatica.
    • WHO/CTD/SIP/98.2Page 10Paragonimus westermaniParagonimiasis occurs in Asia, Africa and the western hemisphere. Theadult worms are encapsulated in the tissues of the lungs and eggs aredischarged in sputum and in faeces. The egg is moderately large, ovoid inshape, has a thick, brown shell and prominent operculum (Slide 33). It isunembryonated when found in sputum or faeces. It measures 80-120 µm by45-70 µm. Other species of Paragonimus infect people in various parts ofthe world. The eggs are all very similar in appearance but differ in size.This egg (Slide 34) of Paragonimus uterobilateralis which occurs in Africaserves as an example.3. Overview of CestodesThe adult cestodes live in the human intestine and those of interest hereproduce eggs which are found in faeces.Taenia solium and Taenia saginataThe adults, as indicated above, live in the intestine and are very large worms,i.e. several meters in length. Proglottids as well as eggs appear in faeces.The eggs of the two species are identical (Slide 35); they are round to ovalin shape, measuring 35-43 µm in diameter and have a thick, radially-striatedshell. The egg contains a 6-hooked embryo called an oncosphere. Theseeggs must be handled with extreme care because the egg of Taenia solium isinfective to humans and produces cysticercosis.Hymenolepis nanaThe adult parasite, found in the intestine, is very small, only a fewcentimeters long. The egg is unique in its appearance (Slide 36). It is small,measuring 30-47 µm in diameter with a thin, colourless shell. Themembrane surrounding the hexacanth embryo has 4-8 filaments arising fromeach pole that fill much of the space between the embryo and the shell (Slide37).
    • WHO/CTD/SIP/98.2 Page 11Hymenolepis diminutaThis tapeworm is a natural parasite of rats but also infects humans,especially children. The adult which measures up to 60 cm in length,produces eggs which pass in faeces. The egg, which resembles that ofHymenolepis nana, is larger measuring 70-85 µm by 60-80 µm and containsa hexacanth embryo (Slide 38). The shell is thick and usually brown incolour. There are no polar filaments emanating from the surface of thehexacanth embryo. In this illustration (Slide 39), the two species ofHymenolepis are shown together to illustrate their differences.Diphyllobothrium latumThis tapeworm, which lives in the intestine, measures several meters inlength. It is found in temperate climates rather than the tropics. Its egg ispassed in faeces. The egg of Diphyllobothrium latum differs from othertapeworms in that it has an operculum (Slide 40). It is ovoid in shape,measures 58-75 µm by 45-50 µm and is unembryonated when found infaeces. There is a small knob on the abopercular end. Sometimes this egg isconfused with that of Paragonimus spp. (Slides 33 and 34).4. Laboratory diagnosis of helminth parasitesA calibrated ocular micrometer, a measuring device, for the microscope is anessential tool for the microscopist. It provides a mean of accuratelymeasuring objects such as eggs, larvae or protozoan cysts. Detailedinstructions for calibration of the ocular micrometer are provided in theBench Aids. Read it carefully and follow the instructions closely. Thelearners will have an opportunity to measure eggs, etc. in the faecal samplesthey will examine. The relative sizes of helminth eggs are shown on theback of Plate 4 of the Bench Aids. Frequently eggs and/or larvae are presentin sufficient numbers to be directly observed in a faecal smear of one or twomg volume. The procedure for performing faecal smears is outlined andillustrated on the back of Plate 1 of the Bench Aids (Slides 41, 42 and 43).Whilst direct smears will often detect helminth eggs, it is usually moreefficient to do a simple concentration procedure to avoid overlookingparasites that may be present in very small numbers. In some situations,such as large community-based surveys, specific objectives are limited todetection of schistosome or soil-transmitted nematode infections.
    • WHO/CTD/SIP/98.2Page 12A modification of the direct smear procedure, the Kato-Katz technique, isespecially useful for field surveys for these infections because it also givesan estimation of the intensity of infection. Detailed instructions forperforming the concentration technique is found on the reverse side of Plate2 of the Bench Aids, and Slides 44, 45, 46 and 47 illustrate the formalin-ether/ethyl-acetate/gasoline concentration procedure. The Kato-Katzprocedure is outlined on the back of Plate 3 of the Bench Aids and Slides 48,49, 50, 51, 52 ,53, 54 and 55 show how to perform the Kato-Katz technique.In part VIII - Inventory of Slide Set - there is a detailed explanation of thediagnostic technique following the texts on the backs of Plates 1 to 3 of theBench Aids.The following slides demonstrate the appearance of common helminth eggsin Kato-Katz preparations:Slide 56 A. lumbricoides, fertile and infertile eggs, with a T. trichiura egg in the middleSlide 57 A. lumbricoides, normal and decorticated eggsSlide 58 T. trichiura eggSlide 59 A. lumbricoides and hookworm eggsSlide 60 A. lumbricoides and T. trichiura eggs.A. lumbricoides and T. trichiura eggs will remain visible and recognizablefor many months in these preparations. Hookworm eggs clear rapidly, and ifslides are not examined within 30-60 minutes, the eggs no longer will bevisible.The smear should be examined in a systematic manner and the number ofeggs of each species reported. Later multiply by the appropriatemultiplication factor to give the number of eggs per gram of faeces (whenusing a 50 mg template by 20; for a 20 mg template by 50; for a 41.7 mgtemplate by 24). With high egg counts, to maintain a rigorous approachwhile reducing reading time, the Stoll quantitative dilution technique with0.1 N NaOH may be recommended.
    • WHO/CTD/SIP/98.2 Page 13VII MEDICALLY RELEVANT PROTOZOA1. Overview of intestinal protozoaThe human intestinal protozoa include non-pathogenic (Entamoeba dispar,Entamoeba coli, Entamoeba hartmanni, Entamoeba polecki, Endolimaxnana and Iodamoeba bütschlii) and pathogenic (Entamoeba histolytica)amoebae, non-pathogenic (Chilomastix mesnili and Pentatrichomonashominis) and pathogenic (Giardia lamblia [intestinalis] and Dientamoebafragilis) flagellates and the pathogenic ciliate parasite, Balantidium coli. Inaddition, human intestinal coccidian parasites producing human diseaseinclude Cryptosporidium parvum, Cyclospora cayetanensis and Isosporabelli. Representatives of a separate phylum, the microspora, include variousgenera and species of microsporidian organisms that cause diseaseprincipally in immunocompromized individuals, such as Enterocytozoonbieneusi, Encephalitozoon intestinalis, Encephalitozoon hellem and others.The importance of the recognition of non-pathogenic (commensal) amoebaeand flagellates lies in the fact that these organisms are indicative of faecal-oral transmission having occurred. When these organisms are found in stoolsamples, it is important to be on the lookout for the possible presence ofpathogenic species. All of the major amoebae found in the intestinal tracthave both trophozoite and cyst stages in their life cycles. Of the intestinalflagellates, G. lamblia (intestinalis) and C. mesnili have trophozoites andcysts, whereas D. fragilis and P. hominis have only a trophozoite stage andlack a cyst stage. The intestinal coccidians (C. parvum, C. cayetanensis andI. belli) all produce cyst stages (known as oocysts) which are excreted infaeces. Microsporidian organisms produce resistant spores which areexcreted in faeces, urine or other bodily secretions.
    • WHO/CTD/SIP/98.2Page 14a. Intestinal amoebaeA 1997 WHO/PAHO/UNESCO Expert Consultation on Amoebiasis1 madeseveral conclusions including:• Biochemical, immunological and genetic data now indicate that there are two species with the same morphological characteristics - E. histolytica and E. dispar - previously known as pathogenic and nonpathogenic E. histolytica respectively. Only E. histolytica is capable of causing invasive disease. In future, the name E. histolytica should only be used in this sense.• When diagnosis is made by light microscopy, the cysts of the two species (10-16µm in diameter) are indistinguishable and should be reported as E. histolytica/E. dispar.• Trophozoites with ingested red blood cells in fresh stool or other specimens and trophozoites in tissue biopsies are both strongly correlated with the presence of E. histolytica and invasive disease.E. histolytica is invasive and may cause disease within the wall of the colonresulting in ulcer formation. Trophozoites of E. histolytica can phagocytizeerythrocytes and they are the only intestinal amoeba to do so (Slides 61 and62). Trophozoites without erythrocytes in their cytoplasm can also be found(Slides 63 and 64) and should be reported as E. histolytica/E. dispar.E. histolytica trophozoites can disseminate via the bloodstream or directtissue spread to other organs and tissues, including the liver, lung, kidney,brain, skin and diaphragm. Cysts of E. histolytica/dispar excreted in faecesmay contain 1 or 2 nuclei (immature cysts - Slides 65, 66 and 67) or 4 nuclei(mature cysts - Slides 68, 69 and 70). Cysts of E. histolytica/E. dispar oftencontain chromatoid bodies with rounded ends (Slides 67, 69 and 70).There are a number of non-pathogenic intestinal amoebae including E. coli(Slides 71, 72, 73, 74, 75 and 76), E. polecki (Slides 77, 78 and 79),E. hartmanni (Slides 81, 82, 83, 84, 85 and 86), Endolimax nana (Slides 88,89 and 90) and I. bütschlii (Slides 91, 92, 93 and 94).All of the these amoebae can be morphologically distinguished from eachother on the basis of morphological features such as size, morphology of the1 WHO, 1997. WHO News and Activities. Entamoeba taxonomy. Bulletin of the World HealthOrganization, 1997, 75, pp 271-292
    • WHO/CTD/SIP/98.2 Page 15nucleus, granularity and inclusions in the cytoplasm, and a number of nucleiin cysts.There is an amoeba that lives in the oral cavity of humans, Entamoebagingivalis, which has only a trophozoite stage (Slide 95); this organismappears to be non-pathogenic and is rarely found.b. Intestinal flagellatesG. lamblia (intestinalis) and D. fragilis are the two medically importantflagellates. G. lamblia (intestinalis) parasitizes the small intestine where itsclinical manifestations may range from asymptomatic to acute and chronicdiarrhoeal conditions. The pear-shaped trophozoite measures 10-20 µmlong, has two nuclei and eight flagella, four of which are lateral, two verticaland two that trail posteriorly. The trophozoite has a concavity or bowl-shaped depression (the “sucking disk”) which occupies the ventral surface ofthe anterior part of the body (Slides 96 and 97). Living trophozoites have acharacteristic tumbling kind of motility when viewed in direct smears insaline prepared from fresh faeces. The cysts of G. lamblia (intestinalis) areoval and measure 8-19 µm. Mature cysts have 4 nuclei and the cytoplasmcontains numerous fibrils (Slides 98, 99 and 100). D. fragilis appears tooccasionally cause diarrhoea in some individuals. This amoeba-likeorganism has no visible flagella and may be confused with amoebae. It onlyexists in the trophozoite stage; a cyst stage has not been described.Trophozoites contain one or more often two nuclei (Slides 101, 102, 103,and 104). In Slide 105, E. histolytica/E. dispar is seen together with atrophozoite ofD. fragilis. The nuclei often have fragmented karyosomes.The most common non-pathogenic intestinal flagellates include C. mesniliand P. hominis. C. mesnili trophozoites are 10-15 µm long, have 3anteriorly directed flagella, a cytostomal groove at the broader, anterior partof the organism, and a single nucleus (Slides 106 and 107).Cysts of C. mesnili are lemon-shaped, uninucleate and measure 6-10 µmlong (Slides 108, 109, 110 and 111). P. hominis lacks a cyst stage and theuninucleate trophozoites are from 7-23 µm long (Slides 112 and 113).
    • WHO/CTD/SIP/98.2Page 16c. CiliatesB. coli is the only human ciliate parasite, living in the colon and appendix.Trophozoites are large (50-200 µm long), move with a rotary, boringmovement and have two nuclei, one of which is prominent and large and theother, small and infrequently visible (Slides 114 and 115). Balantidiasis canbe a severe and fatal disease due to trophozoite colonization of the bowelwall. Cysts are 50-70 µm in diameter (Slide 116).d. Intestinal coccidiaIntestinal coccidian infections of humans are caused by C. parvum,C. cayetanensis and I. belli. All of these have faecal-oral transmission andcan be found in individuals who are immunocompetent as well as in thosewho are immunocompromized (AIDS or other immunodeficiencysyndromes). Cryptosporidiosis produces a more severe and prolongeddisease in patients with AIDS. C. cayetanensis infection is also an importantcause of diarrhoeal disease in immunocompetent individuals. C. parvuminfection is diagnosed by demonstrating round, sporulated oocysts, 4-6 µmin diameter, in faeces. These oocysts are difficult to recognize, especiallywhen present in small numbers in wet mounts prepared from fresh faeces(Slide 117). In fresh smears, the oocysts are retractile and contain a numberof dark granules. However, oocysts of C. parvum are most readily detectedin faecal smears stained by acid-fast stains (Ziehl-Neelsen or Kinyounstains). In acid-fast stained preparations, the red-staining oocysts can bereadily differentiated from green-staining yeasts which are of similar sizeand shape. In these preparations, the oocysts stand out as pink (Slide 118) orred-staining cysts which contain numerous dark staining granules (Slide119). C. parvum oocysts generally are not well stained in routine trichrome-stained faecal smears but occasionally do demonstrate well the 4 sporozoitespresent in the infective oocysts (Slide 120). Oocysts of C. parvum are notstained by iodine.
    • WHO/CTD/SIP/98.2 Page 17C. cayetanensis oocysts must be differentiated from those of C. parvum.C. cayetanensis oocysts are larger, 8-10 µm in diameter, and are notsporulated when excreted in faeces (Slides 121 and 122). In acid-fast stainedfaecal smears, the oocysts of C. cayetanensis are variable in their stainingreaction (Slides 123, 124 and 125). Oocysts may appear as unstained ,wrinkled, round spheres, or stain from a light pink to darker red. Theoocysts of C. cayetanensis can be detected in direct smears from fresh faeceson the basis of their size and refractility.Infection with I. belli occurs both in immunocompetent andimmunocompromized individuals but the disease is more prolonged andsevere in the latter group. Diagnosis is made by demonstrating typical large(20-33 µm long by 10-19 µm wide), thin-walled, unsporulated oocysts infaeces (Slide 126). Infections can be diagnosed by direct wet mountexamination or by flotation or sedimentation concentration procedures. Inacid-fast stained faecal smears, the sporoblast within the oocyst stains redand frequently red stain is deposited on the outside of the thin oocyst wall(Slides 127 and 128).e. Microsporidian infectionsVarious genera of the phylum microspora have been shown to cause humandisease, most frequently in individuals infected with AIDS.Two microsporidians, Enterocytozoon bieneusi and Encephalitozoonintestinalis, infect the intestinal tract and produce diarrhoea. Unlike theamoebae and flagellates which produce cysts and the intestinal coccidianswhich produce oocysts, characteristic spores are produced bymicrosporidians. Spores aretypically oval, small (1-3 µm long) and difficult to find in faecalexamination. The best means of diagnosis is staining faecal smears by amodification of the standard trichrome stain; in this modification, one of thestain components, chromotrope 2R, is increased in concentration. The sporewall stains a bright pink-red colour and many of the spores demonstrate ared, belt-like stripe that encircles the spore equatorially. Spores may alsooccur in urine and other bodily secretions (Slide 129). Slide 120 shows thespores in a calcofluor white-KOH preparation with ultraviolet illumination.
    • WHO/CTD/SIP/98.2Page 182. Laboratory diagnosis of protozoan infectionsTrophozoites and cysts of the intestinal amoebae, flagellates and ciliates canbe found and identified best in permanently stained faecal smears.Trophozoite stages are most often found in watery or diarrhoeic faecalspecimens and usually cysts are not seen in such specimens. On the otherhand, cysts are the stage typically found in formed faecal specimens. Amixture of trophozoites and cysts may occur in softer and semi-formedfaeces.In direct smears of faeces in saline, motile trophozoites may be found.A motile amoebic trophozoite containing red blood cells is immediatelyidentifiable as E. histolytica. Motile amoebic trophozoites that do notcontain ingested erythrocytes are more difficult to classify and are bestdiagnosed in permanently stained smears as all cysts are observed. Althoughexperienced technologists can often identify species accurately in wet mountfaecal preparations, permanently stained smears are superior to saline- oriodine-stained wet mounts.Oocysts of the intestinal coccidians can be identified in wet mount faecalpreparations, principally on the basis of size or shape. They typically do notstain well with trichrome or iron haematoxylin. The use of acid-fast stainingof faecal smears is superior for demonstrating these oocysts. The extremelysmall size of microsporidian spores makes their identification difficult underany circumstances. Modification of the trichrome stain by increasing theamount of the stain components and increasing the time for staining aids indemonstrating the spores in faeces.Flotation and sedimentation faecal concentration procedures are not usefulfor demonstrating trophozoite stages of the intestinal protozoa but can behighly efficient for demonstrating cyst stages.
    • WHO/CTD/SIP/98.2 Page 19Detailed instructions for performing the direct faecal smear, formalin-ether/ethyl acetate/gasoline concentration technique, are given on the reverse sideof Plates 1 and 2 of the Bench Aids. Slides 41 to 47 illustrate the techniques.The permanent stains for faecal smears are described as on the reverse sideof Plate 5 of the Bench Aids.a. Permanent stains for faecal smearsTrichrome stainUse: Very good stain for fresh and PVA (polyvinyl alcohol fixative)preserved faecal smears: does not give good staining results with SAF(sodium acetate, acetic acid, formalin) preservation.Preparation: Add 10 ml of glacial acetic acid to 6 g of chromotrope 2R,3 g of light green SF and 7 g of phosphotungstic acid in a clean flask. Swirlto mix and let stand for 30 min. Add 1000 ml of distilled water and mixthoroughly; the stain should be a deep purple. Store in a glass-stopperedbottle; the stain is stable and is used undiluted.Staining procedure: Place slides, fixed in either Schaudinn’s fixative orPVA, into 70% alcohol for 2 min. Add Lugol’s diluted iodine solution to70% ethanol to produce a colour of strong tea: place slides in the solutionfor 5 min. Place slides in two changes of 70% alcohol. Stain slides inundiluted trichrome stain for 10 min. Remove slides, drain thoroughly, andplace them in 90% acidified alcohol (prepared by adding 4.5 ml of glacialacetic acid to 1 litre of 90% ethanol) for 2-3 seconds. Dip slides in 95%alcohol to rinse and then dehydrate through 100% ethanol and xylene orthrough carbol-xylene mixture. Using resinous mounting medium, place acoverslip on the smear.Iron haematoxylin stainUse: Very good stain for fresh, PVA- or SAF-preserved faecal smears.Preparation:Stock solution A: dissolve 1 g of haematoxylin crystals in 100 ml of 95%alcohol; allow solution to stand in light for 1 week and then filter.Stock solution B: mix 1 g of ferrous ammonium sulfate, 1 g of ferric
    • WHO/CTD/SIP/98.2Page 20ammonium sulfate and 1 ml of hydrochloric acid in 97 ml of distilled water.Prepare a working solution by combining 25 ml each of stock solutions Aand B; prepare at least 3-4 h prior to staining. Prepare picric acid solutionfor destaining by adding 25 ml of saturated aqueous picric acid to 25 ml ofdistilled water.Staining procedure: Place slides into 70% alcohol for 5 min; into 50%alcohol for 2 min; into tapwater for 5 min; into working haematoxylin stainsolution for 10 min; into distilled water for 1 min; into picric acid solutionfor 1 min; into running tapwater for 10 min; into 70% alcohol containing1 drop of ammonia for 5 min; and into 95% alcohol for 5 min. Dehydratethrough 100% ethanol and xylene or through carbol-xylene mixture. Usingresinous mounting medium, place a coverslip on the smear.Modified Ziehl-Neelsen technique (acid-fast stain)Use: For detection of C. parvum, C. cayetanensis, and other coccidianinfections.Reagents: Carbol-fuchsin, formalin, HCl-ethanol solution, glycerol-malachite green (or methylene blue) solution, HCl-methanol solution. Forpreparation of reagents, see the WHO publication Basic laboratory methodsin medical parasitology, 1991.Staining procedure: Prepare a thin smear of faeces; air-dry and fix inmethanol for 2-3 min. Stain with cold carbol-fuchsin for 5-10 min.Differentiate in 1% HCl-ethanol until colour ceases to flow out of smear.Rinse in tapwater. Counterstain with 0.25% malachite green (or methyleneblue) for 30 sec. Rinse in tapwater. Blot or drain dry.
    • WHO/CTD/SIP/98.2 Page 21VIII Inventory of Slide Set2Slide 1 (Plate 1, Fig. 1)Slide 2 (Plate 1, Fig. 2) Normal fertile Ascaris lumbricoides eggs measure 55-75 µm by 35-50 µm, are golden yellow to brown in colour and are in the single cell stage when passed in faeces. The egg has conspicuous mamillations on its surface.Slide 3 (Plate 1, Fig. 4)Slide 4 (Plate 1, Fig. 5) Typical infertile A. lumbricoides eggs in faeces. These eggs are elongated and much larger in size (85-95 µm by 43-47 µm), have a thin shell and a grossly irregular mamillated surface. The content of the egg is usually granular and lacks any organization.Slide 5 (Plate 1, Fig. 6) Fertile and infertile eggs of A. lumbricoides in a Kato-Katz preparation. Note the conspicuous differences between the two.Slide 6 (Plate 1, Fig. 7) Sometimes normal fertile A. lumbricoides eggs lack the mamillated layer and are referred to as “decorticated” eggs. The microscopist must be careful not to confuse these eggs with those of other helminths of similar size.2 The slide set used to illustrate the manual is based on the Bench Aids. However, the slides are not in thesame order and additional slides have been included. Slides have been arranged and numbered accordingto the sequence proposed for presentation. Corresponding figures in the Bench Aids have also beenidentified and included. The numbering of the corresponding figures in the Bench Aids follows the samepattern in all plates, i.e. plate number, followed by the sequence on the plate (first figure is on the top left,last figure is on the bottom right). In figures presenting two different photomicrographs, a and b willrefer to the left and right image respectively.
    • WHO/CTD/SIP/98.2Page 22Slide 7 (Plate 2, Fig. 2)Slide 8Slide 9 Typical Trichuris trichiura eggs measure 50-55 µm by 22-24 µm, have a brown, smooth shell, bipolar prominences (plugs) and contain a single cell ovum ( Slide 7 and 8). Note the differences in size and shape of A. lumbricoides compared to T. trichiura eggs ( Slide 9).Slide 10 (Plate 2, Fig. 4)Slide 11 (Plate 2, Fig. 5)Slide 12 Hookworm eggs found in faeces characteristically are barrel-shaped with a thin, hyaline shell; they measure 60-75 µm by 36-40 µm. They usually are in the 4 or 8 cell stage in fresh faeces (Slides 10 and 12) or in a more advanced stage of cleavage (Slide 11) in faeces that have been kept at room temperature for a few hours.Slide 13 (Plate 2, Fig. 1) A. lumbricoides, T. trichuria and hookworm eggs in the same microscopic field illustrating size and morphological differences in the three species.Slide 14 (Plate 2, Fig. 7) Trichostrongyle eggs resemble hookworm eggs but are larger (75-95 µm by 40-50 µm) and are more elongated in shape. The ovum is in an advanced state of cleavage when discharged in faeces.Slide 15 (Plate 2, Fig. 8) Ternidens deminutus is another strongyle parasite which infects humans, mostly in South Africa. The egg resembles the hookworm egg and measures about 85 x 50 µm. It tends to be in an advanced stage of cleavage when passed in faeces.
    • WHO/CTD/SIP/98.2 Page 23Slide 16 (Plate 2, Fig. 9)Slide 17 Infection with Strongyloides stercoralis is routinely diagnosed by the presence of first-stage rhabditoid larvae in faeces. Larvae measure 180-380 µm long by 14-20 µm in diameter. Larvae have a short buccal capsule, an attenuated tail, and a prominent genital primordium (Slide 16 stained, Slide 17 unstained).Slide 18 (Plate 3, Fig. 3) Schistosoma mansoni eggs in Kato-Katz preparations are easily identified on the basis of size, shape and presence of the lateral spine.Slide 19 (Plate 3, Fig. 1)Slide 20 (Plate 3, Fig. 2)Slide 21 S. mansoni eggs are large, measuring 114-175 µm by 45-70 µm, have a thin, transparent shell, a prominent lateral spine (Slide 19 and 21) and contain a miracidium. Occasionally, the lateral spine may be hidden from view (Slide 20). Gentle tapping on the coverslip usually will reorient the egg exposing the spine to view. Viable eggs have the same appearance in faeces and in rectal biopsies.Slide 22 (Plate 3, Fig. 4)Slide 23 (Plate 3, Fig. 5)Slide 24 Schistosoma japonicum eggs are smaller than those of S. mansoni and Schistosoma haematobium. They measure 70-100 µm by 55-65 µm and tend to be round to oval in shape, have a thin shell and a small inconspicuous lateral spine (Slides 22 and 24). The eggs contain a miracidium. Frequently, faecal debris adheres to the egg surface and may obscure the spine. The orientation of the egg may obscure the spine as well (Slide 23).
    • WHO/CTD/SIP/98.2Page 24Slide 25 Eggs of Schistosoma mekongi, a human schistosome endemic in the Mekong River basin, are morphologically similar to those of S. japonicum but their size range is usually smaller, i.e. 51-78 µm by 39-66 µm.Slide 26 (Plate 3, Fig. 7)Slide 27 (Plate 3, Fig. 8) The eggs of S. haematobium are large, have a terminal spine and contain a miracidium. They measure 112-170 µm by 50-70 µm. These eggs are usually found in urine but occasionally they may also be found in faeces.Slide 28 (Plate 3, Fig. 9) The eggs of Schistosoma intercalatum, a species occurring in humans in West and Central Africa, are usually larger than those of S. haematobium and are typically found in faeces. They measure about 140-240 µm in length and have an equatorial bulge, as illustrated here.Slide 29 (Plate 4, Fig. 1) Clonorchis sinensis eggs measure 27-35 µm long by 12-19 µm wide, have a seated operculum and usually a small protuberance on the end of the egg opposite to the operculum. Often the shell has minute debris adherent to it. Eggs contain a miracidium when passed in faeces.Slide 30 Eggs of the related genus Opisthorchis are similar in size and morphology to those of C. sinensis.Slide 31 (Plate 4, Fig. 3) Fasciola hepatica eggs usually measure 130-150 µm long by 63-90 µm wide, have an inconspicuous operculum, are undeveloped when passed in faeces, and usually have an irregularity in the shell wall at the end opposite the operculum.
    • WHO/CTD/SIP/98.2 Page 25Slide 32 Fasciolopsis buski eggs are similar in size and morphology to those of F. hepatica, except that the irregularity in the shell wall is not present.Slide 33 (Plate 4, Fig. 4) Eggs of Paragonimus westermani measure about 80-120 µm by 45-70 µm, are golden brown in colour, thick shelled, unembryonated when passed in faeces or seen in sputum, and have a prominent operculum. The shell is thickened at the abopercular end.Slide 34 (Plate 4, Fig. 5) Paragonimus uterobilateralis eggs of an African species are usually smaller than those of P. westermani, i.e. 50-95 µm by 35-55 µm; the operculum is less prominent as well.Slide 35 (Plate 4, Fig. 7) Taenia spp. eggs are all virtually identical in size and morphology, about 31-43 µm in diameter, with a thick prismatic-appearing shell wall, and contain a 6-hooked embryo, the onchosphere. Occasionally, a thin, hyaline, primary embryonic membrane may be retained around these eggs.Slide 36 (Plate 4, Fig. 9)Slide 37 Hymenolepis nana eggs are typically spherical to subspherical in shape, measure about 30-47 µm in diameter, have a thin, hyaline shell and contain a 6-hooked onchosphere. There are two polar thickenings on the membrane around the onchosphere from which arise 4-8 filaments that extend into the space between the onchosphere and the shell.
    • WHO/CTD/SIP/98.2Page 26Slide 38 (Plate 4, Fig. 8) The eggs of Hymenolepis diminuta measure 70-85 µm by 60-80 µm, are spherical, yellowish brown in colour, and contain a 6-hooked embryo, the onchosphere. The filaments seen in H. nana extending into the space between the shell wall and the onchosphere are lacking.Slide 39 Note the size difference and the absence of filaments in H. diminuta compared to H. nana.Slide 40 (Plate 4, Fig. 6) Diphyllobothrium latum eggs measure 58-75 µm by 40-50 µm, are unembryonated when passed in faeces and frequently have a knob or small protuberance on the abopercular end of the shell.On Slides 41 to 43 the procedure to perform the direct smear is explained ason the Bench Aids (back of Plate 1).Slide 41 With a wax pencil or other marker, write the patient’s name or identification number and the date at the left-hand side of the slide. Place a drop of saline in the centre of the left half of the slide and place a drop of iodine in the centre of the right half of the slide. (Note: iodine wet mount preparations are most useful for protozoan organisms, less so for helminths.)Slide 42 With an applicator stick or match, pick up a small portion of faeces (approximately 2 mg which is about the size of a match head) and add it to the drop of saline: repeat and add it to the drop of iodine. Mix the faeces with the drops to form suspensions.
    • WHO/CTD/SIP/98.2 Page 27Slide 43 Cover each drop with a coverslip by holding the coverslip at an angle, touching the edge of the drop, and gently lowering the coverslip onto the slide so that air bubbles are not produced. (Note: ideal preparations containing 2 mg of faeces are uniform - not so thick that faecal debris can obscure organisms, nor so thin that blank spaces are present.) Examine the preparations with the 10X objective or, if needed for identification, higher power objectives of the microscope in a systematic manner (either up and down or laterally) so that the entire coverslip area is observed. When organisms or suspicious objects are seen, one may switch to higher magnification to see the more detailed morphology of the object in question.On Slides 44 to 47, the formalin-ether/ethyl-acetate/gasoline concentrationprocedure is explained as on the Bench Aids (back of Plate 2).Slide 44 With an applicator stick, add 1.0 to 1.5 g faeces to 10 ml formalin in a centrifuge tube, stir, and bring into suspension. Strain suspension through the 400 µm mesh sieve or 2 layers of wet surgical gauze directly into a different centrifuge tube or into a small beaker. Discard the gauze. Add more 10% formalin to the suspension in the tube to bring the total volume to 10 ml. Add 3.0 ml of formalin- ether (or ethyl-acetate or gasoline) to the suspension in the tube and mix well by putting a rubber stopper in the tube and shake vigorously for 10 seconds. Place the tube with the stopper removed in centrifuge; balance the tubes and centrifuge at 400-500 x g for 2-3 minutes. Remove the tube from the centrifuge; the contents consist of 4 layers: (a) top layer of formalin-ether (or ethyl-acetate or gasoline); (b) a plug of fatty debris that is adherent to the wall of the tube; (c) a layer of formalin, and (d) sediment.
    • WHO/CTD/SIP/98.2Page 28Slide 45 Gently loosen the plug of debris with an applicator stick by a spiral movement and pour off the top 3 layers in a single movement, allowing to drain inverted for at least five seconds.Slide 46 When done properly, a small amount of residual fluid from the walls of the tube will flow back onto the sediment.Slide 47 Mix the fluid with the sediment (sometime it is necessary to add a drop of saline to have sufficient fluid to suspend the sediment) with a disposable glass pipette. Transfer a drop of the suspension to a slide for examination under a coverslip; an iodine-stained preparation can also be made. Examine the preparations with the 10X objective or, if needed for identification, higher power objectives of the microscope in a systematic manner so that the entire coverslip area is observed. When organisms or suspicious objects are seen, one may switch to higher magnification to see more detailed morphology of the material in question.Slides 48 and 49 show the material needed to perform the Kato-Katzcellophane faecal thick smear technique as in the Bench Aids (back ofPlate 3).Slide 48 Applicator sticks (wooden or plastic); screen (stainless steel, nylon or plastic) 60-105 mesh; template (stainless steel, plastic, or cardboard); templates of different sizes have been produced in different countries. A 50 mg template will have a hole of 9 mm on a 1 mm thick template; a 41.7 mg a hole of 6 mm on a 1.5 mm thick template; a 20 mg a hole of 6.5 mm on a 0.5 mm thick template. The templates should be standardized in the country and the same size of templates should be used to ensure repeatability and comparability of prevalence and intensity data; spatula, plastic; microscope slides (75 x 25 mm).
    • WHO/CTD/SIP/98.2 Page 29Slide 49 Hydrophilic cellophane, 40-50 µm thick, strips 25 x 30 mm in size; flat bottom jar with lid.Slides 50 to 55 show the procedure to perform the Kato-Katz technique as inthe Bench Aids (back of Plate 3).Slide 50 Place a small mount of faecal material on newspaper or scrap paper and press the small screen on top of the faecal material so that some of the faeces will be sieved through the screen and accumulate on top of the screen.Slide 51 Scrape the flat-sided spatula across the upper surface of the screen so that the sieved faeces accumulate on the spatula.Slide 52 Place template with hole on the centre of a microscope slide and add faeces from the spatula so that the hole is completely filled. Using the side of the spatula, pass over the template to remove excess faeces from the edge of the hole (the spatula and screen may be discarded or, if carefully washed, may be reused again).Slide 53 Remove the template carefully from the slide so that the cylinder of faeces is left completely on the slide. Cover the faecal material with the pre-soaked cellophane strip. The strip must be very wet if faeces are dry and less so with soft faeces (if excess glycerol solution is present on upper surface of cellophane, wipe the excess with toilet paper). In dry climates, excess glycerol will retard but not prevent drying.
    • WHO/CTD/SIP/98.2Page 30Slide 54 Invert the microscope slide and firmly press the faecal sample against the hydrophilic cellophane strip on another microscope slide or on a smooth hard surface such as a piece of tile or a flat stone. With this pressure, the faecal material will be spread evenly between the microscope slide and the cellophane strip.Slide 55 Carefully remove slide by gently sliding it sideways to avoid separating the cellophane strip or lifting it off. Place the slide on the bench with the cellophane upwards. Newspaper print can be read through the smear after clarification. Water evaporates while glycerol clears the faeces.Slides 56 to 60 show appearance of A. lumbricoides, T. trichuria andhookworm eggs in Kato-Katz preparations.Slide 56 A. lumbricoides, fertile and infertile eggs with a T. trichuria egg in the middle.Slide 57 (Plate 1, Fig. 8) Normal and decorticated A. lumbricoides egg in a Kato-Katz preparation. Decorticated eggs may be slightly smaller than normal eggs due to the absence of the mamillated layer.Slide 58 T. trichuria egg.Slide 59 A. lumbricoides and hookworm egg.Slide 60 (Plate 1, Fig. 9) A. lumbricoides and T. trichuria eggs. Characteristic features of both are preserved in this preparation.
    • WHO/CTD/SIP/98.2 Page 31Slide 61 (Plate 5, Fig. 2) An elongated trophozoite of Entamoeba histolytica in an unstained saline wet mount preparation demonstrates numerous red blood cells in its cytoplasm. In diarrhoeic and dysenteric stool specimens of individuals with amoebiasis, it is often possible to find amoebae with ingested erythrocytes. Trophozoites with ingested red blood cells in fresh stool or other specimens and trophozoites in tissue biopsies are both strongly correlated with the presence of E. histolytica and invasive disease.Slide 62 (Plate 5, Fig. 8) In this trichrome-stained faecal smear, a trophozoite of E. histolytica contains numerous red-staining erythrocytes in its cytoplasm. The nucleus, with its centric karyosome and fine peripheral chromatin, is partially obscured by the ingested red blood cells but it is located centrally along the lower margin of the amoeboid organism. There is a large glycogen vacuole which compresses the nucleus up against the cyst membrane; several rounded chromatoid bodies are seen around the vacuole.Slide 63 (Plate 5, Fig. 5)Slide 64 (Plate 5, Fig.11) E. histolytica/E. dispar trichrome- and iron haematoxylin-stained trophozoites in a faecal smear. Note the typical nucleus of this species containing a small central karyosome and fine, evenly distributed peripheral chromatin on the nuclear membrane. The cytoplasm is vacuolated.Slide 65 (Plate 5, Fig. 1a) E. histolytica/E. dispar binucleate cyst in MIF (merthiolate-iodine- formalin) wet mount preparation. In immature cysts such as this one, the nuclei are larger than those seen in mature cysts. The large glycogen vacuole lying between the two nuclei often compresses the nuclei against the cyst membrane so that it may be difficult to recognize the karyosomes.
    • WHO/CTD/SIP/98.2Page 32Slide 66 (Plate 5, Fig. 4a) Both uninucleate and binucleate cysts of E. histolytica/E. dispar are seen in the same field of this trichrome-stained faecal smear. In the uninucleate cyst, the large nucleus lies on top of and partially obscures the glycogen vacuole, numerous red-staining chromatoid bodies encircle the vacuole. In the binucleate cyst, the nuclei are smaller and at opposite poles with the glycogen vacuole in the center of this immature cyst. A number of red-staining chromatoid bodies are overlying the vacuole.Slide 67 (Plate 5, Fig. 4b) An uninucleate cyst of E. histolytica/E. dispar, stained with iron haematoxylin, demonstrates a large glycogen vacuole and dark- staining chromatoid bodies. Note the large size of the nucleus.Slide 68 (Plate 5, Fig. 1b) In this iodine-stained mature cyst of E. histolytica/E. dispar, 3 of the 4 nuclei are seen in this plane of focus. In amoebic and other protozoan cysts it is often difficult to demonstrate all nuclei in the same plane of focus. It is recommended that permanently stained slides be prepared on faecal specimens to confirm the diagnosis.Slide 69 (Plate 5, Fig. 7) E. histolytica/E. dispar trichrome-stained mature cyst demonstrating all 4 nuclei and red-staining chromatoid bodies in the center.Slide 70 (Plate 5, Fig. 10) E. histolytica/E. dispar iron haematoxylin-stained mature cyst showing 3 of the 4 nuclei and chromatoid bodies which are not in the same plane of focus.
    • WHO/CTD/SIP/98.2 Page 33Slide 71 (Plate 6, Fig. 1a) A mature cyst of Entamoeba coli is seen in this formalin-preserved, unstained faecal smear. The nuclei of E. coli cysts are readily visible in wet preparations, whether unstained, as here, or in MIF or iodine. All 8 nuclei of the mature cyst usually are not visible in the same plane of focus. Immature, binucleate cysts of E. coli are often of similar size and morphology to those of E. histolytica/E. dispar so that it may be difficult to specify such organisms unless other identifiable cysts or trophozoites are present in the same faecal smear.Slide 72 (Plate 6, Fig. 1b) Two mature cysts of E. coli demonstrate multiple nuclei in this iodine-stained faecal smear.Slide 73 (Plate 6, Fig. 4a)Slide 74 (Plate 6, Fig. 4b) A mature cyst of E. coli is present in this trichrome-stained faecal smear. Five nuclei are easily seen in this plane of focus (Slide 73), whereas in the iron haematoxylin staining only four nuclei can be identified (Slide 74).Slide 75 (Plate 6, Fig. 7)Slide 76 (Plate 6, Fig. 10) E. coli trophozoite in trichrome- and iron haematoxylin-stained faecal smear. The nucleus has a large, centrally located karyosome and the peripheral chromatin is irregular and prominent on the nuclear membrane. The cytoplasm appears highly vacuolated.Slide 77 (Plate 8, Fig. 1) An uninucleate cyst of Entamoeba polecki in a trichrome-stained faecal smear; cysts of this species typically are uninucleate and may contain a dense inclusion mass (as seen here) and/or a large number of chromatoid bodies of varying sizes and shapes. The inclusion
    • WHO/CTD/SIP/98.2Page 34 mass is not glycogen and in iodine wet mounts stains light brown as compared to the dark brown seen with glycogen vacuoles. In this organism, the nucleus is large and has a small karyosome and somewhat peripheral chromatin on the nuclear membrane. The inclusion mass is larger than the nucleus and is situated to the left of it.Slide 78 (Plate 8, Fig. 4) In this trichrome-stained, mature cyst of E. polecki, there are many chromatoid bodies of various sizes and shapes scattered throughout the cytoplasm. The single nucleus is situated on the left side and is partially obscured by the chromatoid bodies. It has a minute central karyosome and irregular peripheral chromatin. The presence of large numbers of chromatoid bodies of various shapes and sizes and the presence of a single nucleus is highly suggestive of E. polecki.Slide 79 (Plate 8, Fig. 7) A trichrome-stained trophozoite of E. polecki is seen here. The nucleus of this species is similar in morphology to that of E. histolytica/E. dispar trophozoites in that the karyosome is often small and centrally located and there is fine peripheral chromatin on the nuclear membrane. However, in E. polecki the nucleus may frequently be irregularly shaped, the karyosome may appear to be lacking, and the peripheral chromatin may be irregular and unevenly distributed on the nuclear membrane.Slide 80 (Plate 5, Fig. 3a)Slide 81 (Plate 5, Fig. 3b) Entamoeba hartmanni uninucleate cysts are shown in these trichrome- (Slide 80) and iron haematoxylin-stained (Slide 81) faecal smears. Glycogen (Slide 80) and chromatoid bodies are present (Slides 80 and 81).Slide 82 (Plate 5, Fig. 6a) A mature cyst of E. hartmanni demonstrates all 4 nuclei in this trichrome-stained faecal smear.
    • WHO/CTD/SIP/98.2 Page 35Slide 83 (Plate 5, Fig. 6b) A binucleate cyst of E. hartmanni with one nucleus in sharp focus and chromatoid bodies is seen in iron haematoxylin staining.Slide 84 (Plate 5, Fig. 9a) A delicately stained trophozoite of E. hartmanni is seen in this trichrome-stained faecal smear. The small nucleus contains a punctuate karyosome and the nuclear membrane has fine peripheral chromatin. Trophozoites of this species usually take a pale stain in permanently stained faecal smears and they can be easily overlooked if the microscopist scans the slide too rapidly.Slide 85 (Plate 5, Fig. 9b) E. hartmanni trophozoite in iron haematoxylin staining.Slide 86 (Plate 5, Fig. 12) Note the size difference of E. hartmanni and Iodamoeba bütschlii trophozoites in this trichrome staining.Slide 87 (Plate 6, Fig. 3a) Endolimax nana mature cyst in an iodine wet mount. Three of the 4 nuclei are seen, each with a large, brown-staining karyosome.Slide 88 (Plate 6, Fig. 3 b) E. nana mature cysts are stained in MIF, with the top one showing 3 of the 4 nuclei.Slide 89 (Plate 6, Fig. 6a)Slide 90 (Plate 6, Fig. 6b) In the trichrome-stained faecal smear, a mature cyst of E. nana demonstrates 3 of 4 nuclei (Slide 89), whereas in the iron haematoxylin staining all 4 nuclei are seen (Slide 90).
    • WHO/CTD/SIP/98.2Page 36Slide 91 (Plate 6, Fig. 2) I. bütschlii cysts in an iodine wet mount. As is typical for this species, the glycogen vacuoles have a prominent brown colour in such preparations. The nucleus typically is not visible in wet mounts.Slide 92 (Plate 6, Fig. 5a)Slide 93 (Plate 6, Fig. 5b) The typical appearance of I. bütschlii cysts in trichrome- (Slide 92) and iron haematoxylin-stained (Slide 93) faecal smear. The karyosome is large, stains red, and there is no peripheral chromatin on the nuclear membrane. With both trichrome stains (Slide 92) and iron haematoxylin (Slide 93), the vacuole remains unstained.Slide 94 (Plate 6, Fig. 8) An elongated I. bütschlii trophozoite in a trichrome-stained faecal smear. The nucleus shows the typical large, red-staining karyosome and the nuclear membrane lacks peripheral chromatin.Slide 95 (Plate 8, Fig. 2) Entamoeba gingivalis trophozoite in an iron haematoxylin-stained smear made from material taken from the parodontal space of the oral cavity. Typically, these non-pathogenic amoebae occur in the mouth of patients who have parodontitis. As in this specimen, the nucleus is E. histolytica/E. dispar-like, in having a small, central karyosome and fine peripheral chromatin on the nuclear membrane. The cytoplasm of these trophozoites typically contains leukocytes in varying stages of digestion (as seen here) as well as bacteria and other detritus. Trophozoites of this species have also been reported from smears made from the cervix and vagina of women utilizing intrauterine-contraceptive devices. E. gingivalis has no cyst stage.
    • WHO/CTD/SIP/98.2 Page 37Slide 96 (Plate 7, Fig. 7) Giardia lamblia (intestinalis) trophozoite in trichrome-stained faecal smear. The characteristic pyriform shape and two anteriorly positioned nuclei on either side of the paired, longitudinally oriented axonemes readily identify this organism.Slide 97 (Plate 7, Fig. 10) Three G. lamblia trophozoites are seen in ventral views and two in lateral aspect (iron haematoxylin staining).Slide 98 (Plate 7, Fig. 1) Several G. lamblia cysts are seen in this iodine wet mount prepared from a flotation concentration procedure. The characteristic shape and appearance of these cysts demonstrating nuclei, axonemes and median bodies is diagnostic.Slide 99 (Plate 7, Fig. 4a)Slide 100 (Plate 7, Fig 4b) Mature cyst of G. lamblia, two of the 4 nuclei, axonemes and the median body are evident (Slide 99 trichrome, Slide 100 iron haematoxylin). A halo around the organism is due to the shrinkage of the organism during fixation (Slide 99).Slide 101 (Plate 7, Fig. 3a)Slide 102 (Plate 7, Fig. 3b) In these trophozoites of Dientamoeba fragilis in a trichrome-stained faecal smear, two nuclei are seen, with one of them being more prominent than the other. Trophozoites of this species may have one or two nuclei, with the binucleate forms being more frequent. The karyosomes within the nuclei are variable in appearance; often they are fragmented into 3 to 8 pieces but in other instances they may appear as a single mass. There is no peripheral chromatin on
    • WHO/CTD/SIP/98.2Page 38 the nuclear membrane. This organism has no cyst stage and its exact manner of transmission has yet to be determined. With both trichrome and iron haematoxylin stains, it is characteristic for these trophozoites to take a pale stain which results in their being overlooked when smears are scanned too rapidly.Slide 103 (Plate 7, Fig. 6a) This iron haematoxylin-stained D. fragilis trophozoite has a single nucleus and a karyosome which is clearly fragmented into 3 pieces.Slide 104 (Plate 7, Fig. 6b) A binucleate trophozoite of D. fragilis in an iron haematoxylin- stained faecal smear. Both nuclei demonstrate fragmentation of their karyosomes into 3 or 4 pieces.Slide 105 (Plate 7, Fig. 9) A binucleate trophozoite of D. fragilis which is more delicately stained (trichrome) is seen between an E. histolytica/E. dispar trophozoite, and a smaller, uninucleate cyst of E. histolytica/E. dispar containing chromatoid bodies.Slide 106 (Plate 7, Fig. 8) Two pale-staining trophozoites of Chilomastix mesnili are seen in this trichrome-stained faecal smear. They have a pyriform shape which tapers to a point at the posterior end and is most clearly seen in the organism on the right. The single nucleus is located at the rounded anterior end of the trophozoites.Slide 107 (Plate 7, Fig. 11) C. mesnili trophozoite iron haematoxylin-stained shows finely pointed posterior end. Note the nucleus at the anterior end.
    • WHO/CTD/SIP/98.2 Page 39Slide 108 (Plate 7, Fig. 2a)Slide 109 (Plate 7, Fig. 2b) In this iodine wet mount preparation, the typical lemon-shaped appearance of C. mesnili cysts are seen. At higher magnification (Slide 109), there is a clear, nipple-like prominence at the anterior end of the cyst, a single nucleus on the left side, and a faint outline of the cytostome visible to the right of the nucleus.Slide 110 (Plate 7, Fig. 5a)Slide 111 (Plate 7, Fig. 5b) C. mesnili cysts in trichrome- (Slide 110) and iron haematoxylin- staining (Slide 111) demonstrate the lemon-shaped appearance, the nucleus and the outline of the cytostome to the right of the nucleus.Slide 112 (Plate 7, Fig. 12a)Slide 113 (Plate 7, Fig. 12b) In this trichrome-and iron haematoxylin-stained faecal smear a trophozoite of Pentatrichomonas hominis (formerly identified as Trichomonas hominis) is seen. The organisms demonstrate the single, anteriorly placed nucleus and the prominent axostyle which is directed posteriorly and extends beyond the posterior end. In stained specimens it is often possible to see a series of longitudinally oriented granules (hydrogenosomes) adjacent to the axostyle. This flagellate has no cyst stage. Trophozoites do not always stain well with permanent stains and diagnosis is often best made by finding the motile trophozoites in freshly passed diarrhoeic infection stools.Slide 114 (Plate 8, Fig. 6) The large trophozoite of Balantidium coli is seen in this MIF wet mount. The cytostome is visible at the top of the organism and the large clear area at the bottom is the macronucleus. Cilia are see on the surface.
    • WHO/CTD/SIP/98.2Page 40Slide 115 (Plate 8, Fig. 9) A trichrome-stained trophozoite of B. coli. The cytostome is seen at the top of the organism and the macronucleus is the dark-staining structure located in midbody. Cilia are visible on the surface as hair- like projections.Slide 116 (Plate 8, Fig. 3) A cyst of B. coli, the only ciliate parasite of humans, in an unstained wet mount of formalin-preserved faeces. The large macronucleus is visible as a clear area at the right side of the cyst.Slide 117 (Plate 9, Fig. 1) Four oocysts of Cryptosporidium parvum are seen in this wet mount preparation from formalin-preserved faeces. The small size of these oocysts (4-6 µm) and the presence of black granules within them are diagnostic for these organisms. However, confirmation of the diagnosis is best accomplished by acid-fast stains of faecal smears. Although not visible here, these infective oocysts contain four sporozoites when excreted in faeces.Slide 118 (Plate 9, Fig. 7)Slide 119 (Plate 9, Fig. 4) Various modifications of acid-fast stains can be used for demonstrating C. parvum oocysts; organisms will vary in colour from dark red to light pink but the black granules are usually readily visible with all of the stain modifications used (Slide 118). In this acid-fast stained faecal smear, 3 oocysts of C. parvum take an intense red colour and show the presence of the black granules (Slide 119).Slide 120 (Plate 9, Fig. 10) C. parvum oocyst do not always stain with trichrome, but when they do, the four sporozoites within them can be seen, as illustrated here.
    • WHO/CTD/SIP/98.2 Page 41Slide 121 (Plate 9, Fig. 2a)Slide 122 (Plate 9, Fig. 2b) Cyclospora cayetanensis unsporulated oocysts are visible in this wet mount preparation from formalin-preserved faeces. These oocysts must be differentiated from the similarly appearing oocysts of C. parvum. C. cayetanensis oocysts are approximately twice the size (8 to 10 µm) of the oocysts of C. parvum. It takes approximately one week for the oocysts of C. cayetanensis to undergo sporulation and develop two sporocysts containing two sporozoites each within the oocyst which is then the infective stage (Slide 122).Slide 123 (Plate 9, Fig. 5) A group of unsporulated oocysts of C. cayetanensis are seen in this acid-fast stained faecal smear. The oocysts of this species stain variably with acid-fast stains, as seen here, and may be pink to red, bluish or not stained at all.Slide 124 (Plate 9, Fig. 8a)Slide 125 (Plate 9, Fig. 8b) C. cayetanensis oocyst in acid-fast staining. The organism can remain unstained (Slide 124) or typically becomes red-stained (Slide 125).Slide 126 (Plate 9, Fig. 3) An unsporulated oocyst of Isospora belli in a wet mount of formalin-preserved faeces. These oocysts are much larger (20-33 µm long) than the oocysts of either C. parvum or C. cayetanensis. They have a very thin cyst wall and they can be easily overlooked when examining wet mount preparations. Typically, oocysts of I. belli will sporulate outside of the human host to become the infective stage.
    • WHO/CTD/SIP/98.2Page 42Slide 127 (Plate 9, Fig. 6a)Slide 128 (Plate 9, Fig. 6b) An atypical oocyst of I. belli appearing empty as often seen in patients undergoing treatment (Slide 127). In Slide 128, an unsporulated oocyst of I. belli is seen in this acid-fast stained faecal smear. The sporoblast inside the oocyst stains intensely red and there is also pink stain deposition on the outside of the oocyst wall.Slide 129 (Plate 9, Fig. 9) Oval-shaped spores of the microsporidian parasite, Encephalitozoon hellem, are seen in Gram-stained urinary sediment from an HIV- positive patient with disseminated infection. Microsporidiosis is an opportunistic infection increasingly associated with patients having the acquired immunodeficiency syndrome (AIDS) or other immunocompromized conditions. These spores are approximately 1 to 2 µm in length and not readily found or recognized unless specialized staining techniques are utilized.Slide 130 (Plate 9, Fig. 12) Spores of one of the intestinal microsporidians, Enterocytozoon bieneusi or Septata intestinalis, are readily seen by using oil immersion microscopy with ultraviolet illumination on methanol- fixed faecal smears stained with 0.5% Calcofluor white in 10% KOH. The bright white fluorescence of the oval spores makes them readily visible.